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Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 70 for “"Neoproterozoic"”.
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Contributions to the Neoproterozoic Geobiology
… to improve our understanding of the Neoproterozoic Paleobiology. In chapter 1, a comprehensive quantitative analysis of the Ediacara fossils indicates that the oldest Ediacara assemblage "the Avalon assemblage" already encompassed the full range of Ediacara morphospace. A comparable …
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Geological constraints on Neoproterozoic glacial episodes
Neoproterozoic glacial episodes are amongst the most intense glaciations that the Earth has experienced, and are associated with major changes in the Earth System, such as the breakup of a supercontinent, the evolution of complex multicellular life and extreme geochemical perturbations. A …
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Investigating the Putative Diagenetic Origins for Neoproterozoic Sponge Steranes
… 24-ipc has been identified in many late Neoproterozoic sedimentary rocks and oils and notably earlier than the first uncontroversial sponge fossil spicules. The sponge biomarker hypothesis argues that this Neoproterozoic 24-ipc comes from ancient demosponges, which would have implications …
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Hydrocarbon biomarkers for biotic and environmental evolution through the Neoproterozoic-Cambrian transition
The sequence of events over the Neoproterozoic - Cambrian transition that led to the radiation of multicellular organisms has been an issue of debate for over a century. It is a critical interval in the history of life on Earth because it marks the first appearance of all extant animal phyla in the …
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The Neoproterozoic São Francisco Basin, central Brazil: tectonic evolution, paleoclimate, and mineral systems
… hosts sediments deposited during most of the Neoproterozoic Era and so is a critical repository of information concerning the evolution of the late pre-Cambrian world. Detailed study and revision of existing stratigraphy reveals that deposition occurred during separate stages of a complete …
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Paleobiology, Biostratigraphy, and Taphonomy of Neoproterozoic Eukaryotes and Cambrian Animals with Carbonaceous Preservation
… times of early life evolution, including Neoproterozoic and Cambrian. Chapters 2 to 5 in this dissertation present original research that helps to decipher hidden biological structures of various carbonaceous fossils using a series of research methods. An improved understanding of these …
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Geochemical investigation of the co-evolution of life and environment in the Neoproterozoic Era
… on a critical period in Earth's history—the Neoproterozoic Era—when profound environmental shifts potentially catalyzed pivotal eukaryotic evolutionary events. By delving deeper into Neoproterozoic paleoenvironments, I aim at a clearer understanding of life-environment co-evolution in this …
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Studying Redox Conditions of Devonian and Neoproterozoic Oceans Using I/ca Proxy From Bulk Carbonate Rocks
… changes during Devonian in Laurentia and during Neoproterozoic in South China, to investigate the relationship between ocean redox, paleoenvironmental changes and biotic events. Chapter 1 focuses on a Mid-Devonian core from Appalachian Basin. I/Ca ratios are generally stable and high in the …
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Sedimentologic, stratigraphic, and tectonic controls of a mixed carbonate-siliciclastic succession : neoproterozoic Johnnie formation, southeast California
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993.
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Neoproterozoic to Holocene tectonothermal evolution of the southern Cantabrian Mountains NW Iberia, revealed by apatite fission-track thermochronology
… by the Palaeozoic succession, represents as a Neoproterozoic sedimentary basement, the Variscan foreland-hinterland transition. Metamorphic conditions increase from anchizone to greenschist facies coincident with hinterland directed increasing deformation. Unconformable and deformed, …
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A geochemical study of neoproterozoic palaeo-evaporites and their possible role in metallogenesis in the Damara Belt of Namibia
Former evaporite horizons in metamorphic terrains have frequently been referred to as a source for highly saline fluids associated with base metal ore deposits in various parts of the world. Data on the nature of these former evaporites and their associated connate fluids, however, is frequently …
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Vertical and Lateral Facies Architecture of Levees and Their Genetically-Related Channels, Isaac Formation, Neoproterozoic Windermere Supergroup, Cariboo Mountains, B.C.
At the Castle Creek study area, levee deposits are well-exposed over an area of ~2.6 km wide and ~90 m thick. This provides an opportunity to describe their lateral and vertical lithological changes, and accordingly details about their reservoir geometry and stratal continuity. Here, levee deposits …
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Association of S-type and I-type granitoids in the Neoproterozoic Cameroon orogenic belt, Bafoussam area, West Cameroon : geology, geochemistry and petrogenesis
… in west Cameroon is located within the Cameroon Neoproterozoic orogenic belt (north of the Congo craton) which is part of the Central African Fold Belt (CAFB).The evolution of the CAFB is related to the collision between the convergent West African craton, the São Francisco – Congo cratons and …
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Geochemical and Paleontological investigations of the Neoproterozoic-Cambrian Transition: Case Studies on geochemical clast provenance, emerging paleo redox proxies, and ambiguous dubiofossils
The transition from the Neoproterozoic to the early Cambrian world was a critical time in the co-evolution of life and the environment, when dramatic changes in the environment, including global glaciations and rising atmospheric oxygen levels precipitated the conditions in which variety of complex …
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Sedimentology of the Squantum ‘Tillite’, Boston Basin, USA: Modern Analogues and Implications for the Paleoclimate during the Gaskiers Glaciation (c. 580 Ma)
… 580 Ma) has been classically traced along the Neoproterozoic Avalonian-Cadomian Terranes, which are now found scattered around the North Atlantic Ocean. Around 625 Ma these terranes were composed of volcanoes and arc-type basins. ‘Till-like’ diamictite horizons identified within these basins …
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The tectonic evolution of the Southern Granulite Terrane of India and its role in the amalgamation of Gondwana.
… debated issue of all is the existence of a late Neoproterozoic (ca. 550 - 500 Ma) suture zone between the Salem and Madurai Blocks, termed the Palghat Cauvery ShearZone (or alternatively, the Cauvery Shear Zone). The U-Pb zircon geochronology of the orthopyroxene-bearing orthogneisses …
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Chemostratigraphy of the Early Paleoproterozoic carbonate successions (Kaapvaal and Wyoming cratons)
… were of global extent. In common with the Neoproterozoic record, carbonates cap the glacials. However, the relationship between biogeochemical cycling of carbon and ice ages has not been fully appreciated. This research involved the sedimentology and isotope stratigraphy of carbonates and …
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Chemostratigraphic correlation and Pb-Pb dating of carbonate sequences in the external Gariep belt and Kango inlier of the Saldania belt in Namibia and South Africa
Worldwide most Neoproterozoic sequences are characterised by an intimate association of glaciogenic diamictite with marine carbonate deposits, indicating possibly rapid climatic changes from icehouse to greenhouse conditions. Such sequences also occur in the Pan-African Gariep Belt and in the Kango …
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Weathering Pathways and Limitations in Biogeochemical Models: Application to Earth System Evolution
… shown that stabilisation of climate following a Neoproterozoic snowball Earth should take more than 10(7) years, due to long-term geological limitation of global weathering rates. The timescale matches the observed gaps between extreme glaciations at this time, suggesting that the late …
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Supercontinents and glaciation: a perspective from western Gondwana.
… events between diverse, relatively small Neoproterozoic continents that amalgamated Gondwana in a piecemeal fashion over 150 million years, with a series of late Ediacaran–Cambrian orogens that represent the final phase of Gondwana amalgamation. A salient feature of the rocks preserving …
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